When administered to estrogen-treated, rat pituitary cells in monolayer culture, progesterone (P, 10 to the -10 power, (-7)M) enhances gonadotropin release within 2-6h but inhibits secretion after 12h of exposure. Similar P actions occur in vivo and determine LH/FSH release during the reproductive cycle as well as following progestin contraceptives. My research investigates the intracellular mechanisms mediating P control of gonadotroph function. I've examined the role of E and P receptor interactions in this control, characterized P modulation of the bioactivity: immunoactivity ratio (BA:IA) of secreted LH and established that P's quantitative and qualitative actions vary with secretagogue (GnRH, iontophores, PKC activators). This proposal expands upon this work. Studies will examine secretion patterns of individual cells by reverse hemolytic plaque assay to assess if P modulation is directed at a particular gonadotroph sub-population, characterized by gonadotropin content (immunocytochemistry), cell size, or P-processing ability (3-HR5020 autoradiography). Other studies will investigate a potential "second messenger" role for arachidonic acid in GnRH action by correlating GnRH-, iontophore- or PKC-activator-stimulated 3-HAA and gonadotropin release by enriched gonadotroph cultures; P influences will also be examined to ascertain if its actions involve changes in AA formation or metabolism. Additional studies will investigate the influences of P on LH, FSH and inhibin synthesis and LH glycosylation. This work is based on recent reports that prolonged exposures to low [GnRH] activate gonadotropin synthesis in vivo and in vitro and on my findings that P modulates the BA:IA of secreted LH. Chromatofocussing columns will be used to identify the LH isohormones present in or secreted by E+P-treated cells in culture. The uptake of 35S-methionine and 3H-glucoseamine into LH isohormones will be monitored following certain P+secretagogue combinations. A similar format will be followed to examine methionine and glucoseamine incorporation into LH-alpha and LH-beta subunits. These studies have the potential to identify P-induced shifts in BA:IA, the isohormone involved and the subunit at which changes in glyco- sylation take place. The results of these studies will increase our understanding of steroid-neurohormone interaction in the adenohypophysis and will provide information about the molecular mechanisms involved in gonadotropin release.